170 PKOCEEDINGS OF THE AMERICAN ACADEMY. 



from radiation and convection-currents from the walls of the heater. The 

 holes in the glass cover through which the lead-wires and the thermome- 

 ter enter are but little larger than these, so as to prevent loss of vapor. 

 The thermometer is supported by meaus of a cork stopper which rests on 

 the top of the watch glass. The insertion of cork stoppers in the holes is 

 not advisable, as they cause the hot liquid to escape through their pores. 

 The bomb is supported in the heater by means of a brass frame, F, and 

 suspension wires, W, which hang on two steel pins screwed into the 

 walls of the heater. At the top of each of the two suspension wires is a 

 loop, so that by inserting a steel hook in each of these loops, the bomb 

 is easily removed from the bath while still hot. The sides of the heater 

 are well jacketed with asbestos. It is supported on a metal tripod by 

 means of three steel pins, which project through the asbestos covering. 

 It is heated by gas burners below, one sufficing after the bomb and 

 heater have become hot. 



Commercial xylene was first used for the 140° bath, but the pure 

 metaxylene was found to give a more constant temperature and one 

 more uniform in the upper and lower parts of the bomb : to prevent the 

 escape of the vapor, it was necessary in this case to cause water to circu- 

 late through a jacket surrounding one of the condenser tubes. Pure naph- 

 thalene from Kahlbaum was used to give a temperature of 218°, and was 

 found to be an ideal substance, a-bromuaphthalene was employed for 

 the next higher temperature (281°), as it seemed to be the only avail- 

 able substance ; it is not convenient, however, since it decomposes slowly 

 upon boiling with formation of tar and hydrobromic acid (which attacks 

 the outside of the bomb) : it must therefore be frequently removed from 

 the heater and redistilled. The highest temperature (306°) was main- 

 tained with benzophenone, which boils unchanged even after many days 

 of continuous heating. 



4. Thermometers. — The temperature of the liquid xylene bath was 

 measured with an ordinary thermometer reading directly to tenths of a 

 degree, and this was checked from time to time against a standard Ton- 

 nelot thermometer. 



For the higher temperatures French mercurial thermometers, made 

 "by Alvergniat, with a range of 360° and graduation in degrees, were 

 used. By the use of a little reading telescope these thermometers were 

 read with certainty to 0.1°. They were standardized as described in 

 Section VI of this article. The mercury column was always completely 

 immersed in the vapor, and to take a reading the thermometer was 

 quickly raised only enough to render the meniscus visible above the top 



